The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, an internal combustion engine (hereafter, referred to as an “engine”) is equipped with a valve timing adjustment apparatus that can change timing of intake valves and exhaust valves, depending on the operation state of the engine. Such a valve timing adjustment apparatus adjusts the timing of intake valves or exhaust valves by changing a phase angle according to the displacement or rotation of a camshaft connected to a crankshaft usually through a timing belt or a chain, and various types of valve timing adjustment apparatuses have been proposed.
In general, a vane type valve timing adjustment apparatus that includes a rotor having a plurality of vanes freely rotated by working fluid in a housing is generally used.
The vane type valve timing adjustment apparatus adjusts valve timing using a difference in rotational phase generated due to relative rotation in an advance direction or a retard direction of a rotor that is rotated through vanes operated by the pressure of working fluid to an advance chamber or a retard chamber between a full advance phase angle and a full retard phase angle.
We have discovered that a positive torque is generated by friction due to rotation of a cam in opposite direction to the rotational direction of the cam. Meanwhile, a negative torque is generated by restoring force of a valve spring in the same direction as the rotational direction of the cam when a valve starts closing, and the negative force is smaller than the positive torque.